Connectors for optical fiber transmission systems are known in the art. Often times it becomes necessary to arrange a plurality of optical fiber connectors in a panel to facilitate multifiber connections. A very much used ferrule connector for terminating and connecting two optical fibers is one which is referred to as an ST.RTM. connector, ST being a registered trademark of AT&T. The ST connector is disclosed, for example, in U.S. Pat. No. 4,934,785 which issued on Jun. 19, 1990 in the names of T. D. Mathis and Calvin M. Miller.
An ST connector includes a cylindrical plug or ferrule, as it is often called, having a passageway therethrough for receiving an end portion of an optical fiber to be terminated. The ferrule which is received in a barrel that is mounted in a cap is spring-loaded. When two of the ferrules are received end-to-end in a coupling sleeve, for example, one or both of the ferrules is moved along its longitudinal axis during the connection process.
During the connection process, a key which extends radially from the barrel in which an end portion of the ferrule is received is aligned and moved along a keyway in a housing of a coupling as the ferrule is moved into a sleeve disposed within the housing. At the same time, two locking pins which extend radially from the coupling housing are moved into and along camming slots which extend helically from a front end of the cap rearwardly. As the locking pins are moved along the camming slots, the ferrule is moved farther into the sleeve. When each locking pin reaches an end of its associated camming slot, a craftsperson applies forces to the cap to cause it to move rotatably to cause each locking pin to be aligned with a relatively short locking slot which extends from an inner end of the associated camming slot toward a free end of the cap. This pushing motion followed by a rotary motion is often called a bayonet turn. Also, when each locking pin reaches an innermost end of the associated camming slot, the ferrule is at its farthest point within the sleeve from an entrance thereof.
Of course, forces applied to a mating second connector to cause its ferrule to be moved into and along the sleeve to its innermost position must be sufficient to overcome spring forces which tend to cause the ferrule of the other first connector to be biased into the sleeve. In fact, when only a first one of the ferrules is disposed within the sleeve, its innermost end extends beyond the transverse centerline of the sleeve. The transverse centerline of the sleeve is referred to as the optical connection plane. This extension past the optical connection plane is referred to as overtravel. As a result, forces must be applied to the second ferrule to overcome the spring forces of the first ferrule to cause it to moved slightly to allow the second ferrule to be moved past the optical connection plane to that position which corresponds to locking pins reaching the innermost ends of the camming slots of the second connector. After the locking pins are aligned with the relatively short locking slots, the craftsperson allows the spring associated with the second ferrule to force the cap rearwardly to cause the relatively short locking slots to be moved along the locking pins to secure the second connector to the coupling housing and to cause the end of the second ferrule to return to the optical connection plane.
Stringent tolerances are needed in order to ensure that the over-travel and return of the ferrule to the optical connection plane are controlled to achieve a proper connection. It is most desirable that the connection be made without the need to bayonet turn or to turn threadably the connector cap as must be done with some presently manufactured ferrule connectors.
Another problem with the use of prior art ferrule connectors relates to the potential for optical disconnection of optical fiber end faces or of an optical fiber end face and an optical device to which it is connected. It will be recalled that the connector ferrule is biased outwardly of the cap by a compression spring. Should sufficient force be applied inadvertently axially to the optical fiber cable which is terminated by the ferrule in a direction away from the optical connection, the ferrule will be moved in a direction outwardly from the center of the sleeve, causing effectively a significant optical loss and/or disconnection of the optical fiber end faces or of a fiber end face and a device and hence a significant optical loss and/or disconnection of optical transmission.
Also, because of the construction of the housing, the ferrule, upon the application of forces to the cable in a direction transversely of the axis of the connector will result in a turning of the ferrule about a fulcrum located between the center of the sleeve and the end of the cap. This results in a canting of the end face of the ferrule and angular spacing thereof from the other ferrule or device thereby causing an optical disconnection or increased transmission loss.
In another prior art ferrule connector, a non-optical disconnect feature is built into the connector plug arrangement. See U.S. Pat. No. 4,812,009 which issued on Mar. 14, 1989 in the names of A. W. Carlisle, B. V. Darden and C. J. Myers. A cap extender extends longitudinally along the optical fiber cable and includes an externally threaded end which is turned into engagement with an internally threaded cable entrance end of the cap. The portion of the barrel which extends into the cap extender is provided with an annulus which when the cap extender is threaded completely into the cap engages an inner portion of the cap extender, restraining the barrel and the ferrule from movement. Further, the cap extender is used to transfer transverse forces which are applied to the cable from the optical connection and instead transfers them to the connector cap. A conically shaped strain relief portion is disposed about and extends beyond the cap extender into engagement with the jacket of the cable.
One of the problems with this last-described arrangement is that when the cap extender is threaded completely into the cap prior to installation onto the coupling housing, it is impossible to obtain the overtravel needed for each locking pin to travel the complete length of an associated camming slot and be received in a relatively short locking slot. On the other hand, if the non-optical disconnect cap extender is not turned completely into the cap, it becomes somewhat awkward to couple the connector assembly to the coupling housing, as the cap must be grasped by a user to bayonet turn the connector. Holding the cap extender subassembly will cause slipping relative to the cap as forces are applied to the coupling. Furthermore, only one connector having a non-optical disconnect feature may be assembled to a coupling housing in the field. Otherwise, with the cap extenders of both connectors turned threadably completely into associated caps, the last one to be assembled to the housing would cause compressive damage to fiber end faces in the abutting ferrules.
As should be apparent, some prior art connectors exhibit problems that need to be overcome. In one prior art arrangement, forces applied to one cable in excess of approximately two pounds will cause ferrules to decouple or disconnect at the fiber end faces within a coupling housing. The described arrangement having the non-optical disconnect feature overcomes the problem of optical disconnect by limiting ferrule travel away from the optical connection plane; however, it has several limitations. First, the connector assembly cannot be held by the cap extender and strain relief sub-assembly while pushing and rotating onto the coupling when the cap extender is loosely threaded onto the cap. The cap extender will be turned but the cap will not become locked to the coupling. Secondly, if the cap extender is turned in completely into the cap, the locking pins of the coupling housing cannot travel the complete length of the camming slots, preventing installation of the connector.
What is needed and what seemingly is not available is a more effective arrangement to prevent optical as well as mechanical disconnection in a ferrule connector arrangement. Also, the sought after connector should be one which is assembled and secured to a coupling housing with linear motion only. What is sought after and what seemingly is not available is an ST connector which is secured to a coupling housing, with the housing mounted in a panel by a pushing motion without the need to turn the connector relative to the housing, and yet is one which prevents decoupling of the ferrule and housing.